Electrochemical sensors are used to determine the concentrations and identities of various analytes in samples such as fluids and dissolved solid materials. Electrochemical sensors are used in a wide variety of applications, including chemical and biochemical science, occupational safety, medical engineering, process measuring engineering, and environmental analysis. By way of illustration, electrochemical gas sensors are well known for detecting and quantifying toxic gases such as carbon monoxide, hydrogen sulfide, nitrogen oxides, chlorine, sulfur dioxide and the like. Electrochemical aqueous analyte sensors are well known for detecting and quantifying analytes such as hydronium, dissolved oxygen, and halides.
A typical electrochemical sensor has a plurality of electrodes, including two, three, and four or more electrodes. Commonly, an electrochemical sensor includes an auxiliary electrode, reference electrode, and one or more working electrodes. The electrodes are typically fabricated from electrically conductive solid materials, thin films, and liquids. The working electrode provides the surface where the target electrochemical reactions take place. The electrodes are typically arranged in an inert, non-electrically conductive housing which contains sealed electrical contacts to connect the electrodes to an electrochemical controller such as a potentiostat.
The electrodes of an electrochemical sensor provide a surface at which an oxidation or a reduction reaction occurs. The ionic conduction of the analyte solution in contact with the electrode is coupled with the electron conduction of the working and auxiliary electrodes to provide a complete circuit for a current. The reference electrode, such as a silver/silver chloride electrode, provides a reference voltage. As will be appreciated, the auxiliary electrode is typically made of a material having a low work function and has significantly greater surface area than the working electrode. In a typical electrochemical sensor, the analyte to be measured passes via mass transfer from the bulk solution to the sensor housing to a working electrode where a chemical reaction occurs based on the working electrode surface material and the electrical bias applied to the working electrode with respect to the reference electrode. Electrochemical sensors, such as pH sensors, ion selective sensors, and redox sensors, are equipped with electrical conductors to allow electrical signals to be transmitted to and from electrodes contained within the sensor. An electrochemical sensor used for measuring pH, ORP, or other specific ion concentrations is typically comprised of five parts: an analyte sensing working electrode, a reference electrode, a low work function auxiliary electrode, a temporal electrical potential control source, and an amplifier that translates signal into useable information that can be read. The latter two parts are enabled by the use of an electrochemical controller called a potentiostat. Repeated temporal electrical potentials and measurements make up a pattern that the potentiostat applies to the electrodes to provide the operator with chemically significant results.
Current electrochemical potentiostats have a number of design considerations. Research scientists, laboratories and businesses employing custom electrodes to make analytical measurements as part of their operations need an electrochemical tool as easy to use as an electrochemical meter. An electrochemical meter consists of a potentiostat that automatically recognizes a set of electrodes as a sensor, and a sensor is a set of electrodes that make a specific analyte measurement when operated with predefined electrical potentials. An electrochemical meter is easy to use due to the combination of well defined electrical potentials and electrodes that allow for automatic reporting of the target analyte concentration. Potentiostats employed with a user defined electrode set do not provide for means to recognize the same electrode set in discontinuous experiments. The potentiostat should be inexpensive. Capital equipment costs discourage researchers from performing multiple measurement experiments simultaneously. The potentiostat should have intuitive and relatively simple software. Complex software limits the degree of automation and flexibility that the scientist or engineer can implement. The potentiostat should be able to perform long-term experiments, such as experiments that perform and record measurements over weeks, months and years. The emphasis on data collection speed of most potentiostats has placed significant limits on the ability to perform long-term experiments.